1. Technical Field of the Invention
The present invention relates to SOC systems (“System-On-Chip”).
2. Description of Related Art
SOCs are the result of integrating a more complete system on one same chip. Several circuits are grouped together on one same chip to form a single electronic component, thereby avoiding having to use several chips to group the different circuits contributing towards the functioning of one same unit.
Each constituent block of a SOC is called an IP block (for Intellectual Property). An IP block is a virtual assembly of components representing the component integration know-how of a company (semiconductor manufacturer or other). The function to be integrated may be a physical, material function, or a software function (or both at the same time) of specific components. Conventionally, a distinction is made between types of blocks:                so-called “soft” IP blocks (for “software”), with a VHDL model for example (language for computer assisted design allowing a circuit to be modeled and simulated at different abstraction levels) which is used to the synthesize the circuit using a library of pre-characterized cells, and        so-called “hard” IP blocks (for “hardware”) with a technology-targeted layout.        
A third type of IP block, i.e., memories, can be added to these two block types.
SOC systems are likely to play an increasingly greater role in the telecommunications sector in particular. They form a fundamental technology for telecommunications equipment and determine the services which this equipment is able to provide. Technological advance has led to the commercial development of portable systems, i.e., battery-operated. Battery-run products require a sufficient reserve time. This reserve time can be increased by energy savings systems. e.g. idle or standby modes which are currently insufficient.
In parallel, the development of SOCs must also meet requirements for control of circuit consumption.
Several techniques intended to control consumption have been introduced. The principle developed here is not to place the circuit in idle mode but to cut off the power supply to the circuit, or part thereof, when the product or part thereof is not in use.
For as long as it receives power, an electronic circuit consumes energy even if it is not active, chiefly through leakage currents which are responsible for static consumption by the circuit. These leakage currents are increased with the decreasing size of components (transistors).
To optimize power distribution, and hence to save power, solutions have been put forward to split a circuit into several portions and to cut off the power supply to only part of the circuit, i.e., in one or more portions of the circuit not in use.
The electronic system developed in this manner consists of managing several power supply domains, the SOC being provided with means to cut off the supply to inactive parts (domains) of the circuit, while others remain active and hence are powered.
An SOC is an electronic circuit able to execute several functions, e.g., audio and/or video reading on a mobile telephone. Under normal conditions of use, all functions executable by the SOC are not executed simultaneously.
A function is executed by an IP block for example, or by a plurality of IP blocks.
An SOC is also designed as a circuit comprising a sum of power supply domains, called domains. A domain is therefore a sub-part of the SOC system and corresponds to one or several IP blocks, optionally even to only one part of a block in the case of a “soft” IP block.
A domain is therefore able to perform or execute one or more functions and a function may be performed or executed by one or more domains. However, as a general rule, a function is equivalent to a domain.
Power saving consists of cutting off the supply to areas corresponding to a non-used function, which in most cases amounts to cutting off the supply to the domain responsible for the function not in use.
The problem associated with this form of functioning lies in each powering-up of a switched-off domain. It is necessary to control the current consumption peak of the domain so as to avoid damage thereto, and more especially so as not to penalize other domains that are in use, the consumption peak being the peak observed on each powering-up of the domain and used to charge its equivalent capacity.
The prior art contains the document “90 nm low leakage SOC design techniques for wireless applications” published by IEEE (ISBN 0-7803-8904-2/05) under reference ISSCC 2005/SESSION 7/MULTIMEDIA PROCESSING/7.6. The solution proposed in this document consists of designing a SOC system comprising several supply domains and using several modes to save on power supply. The electric supply is distributed using a standard meshing system: a global network to distribute power supply and ground supply throughout the entire SOC, and a sum of local networks reflecting the partitioning into domains. The global network is linked to the local networks via a certain number of switches.
These switches are incorporated inside the domains, staggered at a regular pitch, or around “hard” IP blocks, or both. They operate in cascade one after the other. The switches are embedded inside the domain, in the standard cells, and each switch consists of two PMOS transistors.
A standard cell is a cell which provides a basic logic function, e.g., a CMOS inverter. A “soft” IP block corresponds to an assembly layout of a plurality of standard cells.
The problem with this configuration is that, to ensure power supply, one must reach inside a block of standard cells, inside the domain. In addition, the consumption peak is not fully controlled, since consumption depends in particular on the sequence switching speed of the switches.
There is a need in the art to overcome this shortcoming by proposing a different architecture with which it is possible to power a standard supply domain selectively, while controlling the current consumption peak.